08/15/02

A Guitar Makerīs Note on the Construction of 10-string
Guitarsby Sebastian Stenzel

Anyone who ever started playing
10-string guitar has had to accept that in addition to mastering the actual
creation of sound, there is a problem to solve that doesn't exist in this
dimension on a 6-string guitar: the dampening of unwanted resonances. These
resonances from the additional strings confront the luthier with a
contradiction that is in my opinion the most salient point in the
construction of 10-string guitars: if the guitar has too much sustain, the
player will be busy dampening rather than playing the guitar. If there is
too little sustain, the guitar will be very stiff, lacking capacity of
modulation, and - while functioning well with chords - sound rather boring
when monophonic lines are played. The challenge for the guitar maker is to
find the best compromise between these two poles.
Among the hundreds of guitars that I have scrutinized during
the last fifteen years, there have been a few 10-string guitars, and even
fewer really good ten-strings. It is my habit to take measurements of all
interesting guitars that come into my workshop, and by comparing the data of
different 10-string guitars, I've quickly understood that there is a common
misunderstanding among guitar makers about the construction of 10-string
guitars. Due to the very little energy available to create a guitar sound
(compared e.g. to the violin, where the bow allows a continues input of
energy) the guitar is constructed close to the limits of static stability.
This situation is aggravated by adding four more strings, thereby increasing
the string tension on this fragile structure by approximately 60%. This
seems to frighten many luthier, who strengthen their soundboard in what they
think is an equal measure, assuming a directly proportional relationship of
soundboard thickness and static stability. In reality, the moment of inertia
relevant to the profile of a body depends on the thickness to the third
power. Simply put, every tenth of a millimeter in thickness increases the
static stability considerably. As a result of this misconception, many
ten-strings have been build too much on the safe side. The sensitivity of
the luthier to find the right point of balance when making the soundboard is
challenged just a little more than when building a "normal" guitar.
Back to the problem of resonances: first, it has to be said
that they are unavoidable, even in six-string guitars. In fact, the
phenomena of resonance is the basic principle of amplification of all
acoustic instruments. It is an essential aspect of the art of lutherie to
spread the resonance-peaks so evenly that they do not detract from the
desired tone. What was said before concerning the string tension also holds
true for the resonances: the situation is simply aggravated. The same
details of construction used in six-string guitars to spread resonances
evenly will work in a ten-string guitar too, because the tuning is similar,
and so are the basic dimensions of the guitar body. Technically, a
ten-string guitar is not so different from a six-string as one is easily led
to think, but it will accentuate any faults and weaknesses of a
construction.